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Improved palette handling with saving PNG files.

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Instead of converting alpha to a mask an attempt is made to write a palettised PNG file with an ARGB palette using a maximum of 256 transparency values where formerly just up to one was supported. GIF images with 256 colours and transparency can now also be saved as a palettised PNG instead of true colour, making the image a lot smaller.

Applied (modified) patch by troelsk. Closes #12850.



git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67101 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Dimitri Schoolwerth
2011-03-01 21:29:17 +00:00
parent 548fa9c1eb
commit 8529b0b909
2 changed files with 164 additions and 177 deletions
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97
tests/image/image.cpp
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@@ -71,6 +71,7 @@ private:
CPPUNIT_TEST( SizeImage );
CPPUNIT_TEST( CompareLoadedImage );
CPPUNIT_TEST( CompareSavedImage );
CPPUNIT_TEST( SavePNG );
CPPUNIT_TEST( SaveAnimatedGIF );
CPPUNIT_TEST( ReadCorruptedTGA );
CPPUNIT_TEST( GIFComment );
@@ -82,6 +83,7 @@ private:
void SizeImage();
void CompareLoadedImage();
void CompareSavedImage();
void SavePNG();
void SaveAnimatedGIF();
void ReadCorruptedTGA();
void GIFComment();
@@ -1023,77 +1025,78 @@ void ImageTestCase::CompareSavedImage()
CompareImage(*handler, expected24);
CompareImage(*handler, expected32, wxIMAGE_HAVE_ALPHA);
}
}
void ImageTestCase::SavePNG()
{
wxImage expected24("horse.png");
CPPUNIT_ASSERT( expected24.IsOk() );
#if wxUSE_PALETTE
CPPUNIT_ASSERT( !expected24.HasPalette() );
#endif // #if wxUSE_PALETTE
wxImage expected8 = expected24.ConvertToGreyscale();
/*
horse.png converted to greyscale should be saved without a palette.
*/
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG), expected8);
/*
But if we explicitly ask for trying to save with a palette, it should work.
*/
expected8.SetOption(wxIMAGE_OPTION_PNG_FORMAT, wxPNG_TYPE_PALETTE);
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
expected8, wxIMAGE_HAVE_PALETTE);
expected8.LoadFile("horse.gif");
CPPUNIT_ASSERT( expected8.IsOk() );
CPPUNIT_ASSERT( expected8.LoadFile("horse.gif") );
#if wxUSE_PALETTE
CPPUNIT_ASSERT( expected8.HasPalette() );
#endif // #if wxUSE_PALETTE
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
expected8, wxIMAGE_HAVE_PALETTE);
/*
Add alpha to the image in such a way that there will still be a maximum
of 256 unique RGBA combinations. This should result in a saved
PNG image still being palettised and having alpha.
*/
expected8.SetAlpha();
width = expected8.GetWidth();
height = expected8.GetHeight();
int x, y;
const int width = expected8.GetWidth();
const int height = expected8.GetHeight();
for (y = 0; y < height; ++y)
{
for (x = 0; x < width; ++x)
{
expected8.SetAlpha(x, y, (x*y) & wxIMAGE_ALPHA_OPAQUE);
expected8.SetAlpha(x, y, expected8.GetRed(x, y));
}
}
/*
Explicitly make known we want a palettised PNG. If we don't then this
particular image gets saved as a true colour image because there's an
alpha channel present and the PNG saver prefers to keep the alpha over
saving as a palettised image that has alpha converted to a mask.
*/
expected8.SetOption(wxIMAGE_OPTION_PNG_FORMAT, wxPNG_TYPE_PALETTE);
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
expected8, wxIMAGE_HAVE_ALPHA|wxIMAGE_HAVE_PALETTE);
/*
The image contains 256 indexed colours and needs another palette entry
for storing the transparency index. This results in wanting 257 palette
entries but that amount is not supported by PNG, as such this image
should not contain a palette (but still have alpha) and be stored as a
true colour image instead.
Now change the alpha of the first pixel so that we can't save palettised
anymore because there will be 256+1 entries which is beyond PNGs limit
of 256 entries.
*/
expected8.SetAlpha(0, 0, 1);
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
expected8, wxIMAGE_HAVE_ALPHA);
#if wxUSE_PALETTE
/*
Now do the same test again but remove one (random) palette entry. This
should result in saving the PNG with a palette.
Even if we explicitly ask for saving palettised it should not be done.
*/
unsigned char red[256], green[256], blue[256];
const wxPalette& pal = expected8.GetPalette();
const int paletteCount = pal.GetColoursCount();
for (i = 0; i < paletteCount; ++i)
{
expected8.GetPalette().GetRGB(i, &red[i], &green[i], &blue[i]);
}
wxPalette newPal(paletteCount - 1, red, green, blue);
expected8.Replace(
red[paletteCount-1], green[paletteCount-1], blue[paletteCount-1],
red[paletteCount-2], green[paletteCount-2], blue[paletteCount-2]);
expected8.SetPalette(newPal);
wxImage ref8 = expected8;
/*
Convert the alpha channel to a mask like the PNG saver does. Also convert
the colour used for transparency from 1,0,0 to 2,0,0. The latter gets
done by the PNG loader in search of an unused colour to use for
transparency (this should be fixed).
*/
ref8.ConvertAlphaToMask();
ref8.Replace(1, 0, 0, 2, 0, 0);
expected8.SetOption(wxIMAGE_OPTION_PNG_FORMAT, wxPNG_TYPE_PALETTE);
CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_PNG),
expected8, wxIMAGE_HAVE_PALETTE, &ref8);
#endif
expected8, wxIMAGE_HAVE_ALPHA);
}
void ImageTestCase::SaveAnimatedGIF()